The present invention is directed to transferring electronic information between two frames (or members) that move in relation to one another, and more specifically to a communication link that utilizes conductive (or contact-type) coupling between the two frames (or members).
Contact-type slip rings have been widely used to transmit electrical signals across frames that move rotationally in relation to each other. Prior art slip rings of this nature have carried signals between a stationary frame and a rotating frame by utilizing a conductive probe or probes (precious metal alloy wipers or composite brushes) on one frame. The conductive probe or probes maintain contact with precious metal plated rings on the other frame during movement. A similar scheme has been used to transfer electrical signals between two frames that move in a non-rotational manner with respect to each other.
In digital systems, data transmission rates of these prior art contacting devices have been limited by impedance mismatch at the wipers or brushes. This impedance mismatch at the contact region causes reflections of a transmitted signal. Subsequent reflections of a reflected signal distort the pulses of the transmitted signal. Distortion of the pulses can appear as jitter, duty cycle variation, dc offset, multiple threshold crossings or other undesirable effects that result in bit errors. As a result, contact-type slip rings have not been used when higher data transmission rates were required.
Slip rings have also commonly been a part of transmission lines that carry analog signals. While an impedance mismatch in the transmission path causes some reflection of any signal, the effect on higher frequency components is more significant. When an analog signal contains high frequency components, distortion of the transmitted signal due to reflections can be severe.
Higher frequency analog transmission and higher bit rate digital transmission has been achieved with fiber optic interfaces. These fiber optic interfaces have included a rotary interface. The rotary interface has included a fiber optic rotary joint that transmits the optical signal across a gap between a rotary frame and a stationary frame. Rotary interfaces that utilize capacitive coupling have also been utilized for higher frequency analog transmission and higher bit rate digital transmission.
A conductive slip ring system, according to an embodiment of the present invention, functions to transfer information electrically between a moving frame and a stationary frame. The conductive slip ring system includes a conductive transmission line and a conductive probe. The conductive transmission line is attached to the stationary frame or the moving frame. The conductive transmission line includes a first portion and a second portion. The first portion includes a first end and a second end. The first end of the first portion is coupled to a first terminator. The second end of the first portion is coupled to a signal source through a first reflection path impedance matching resistor. The second portion includes a first end and a second end. The first end of the second portion is coupled to a second terminator and the second end of the second portion is coupled to the signal source through a second reflection path impedance matching resistor. The second end of the first portion and the second end of the second portion are coupled together by a third reflection path impedance matching resistor. The conductive probe is attached to the moving frame or the stationary frame. The conductive probe contacts the conductive transmission line and provides a communication path between the stationary frame and the moving frame. The conductive probe and the conductive transmission line are on opposing frames.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.